What were they actually feeding it? That's the bit I went off to look up after Ada's plate, because a mould has to eat, same as a starter does, and in 1928 they were coaxing it along in broth like an invalid. Turns out what finally worked was corn steep liquor — the sour water left over when you soak corn at the mill before you grind it. Waste. Sharp, yoghurty, silage-ish. The Peoria lab had it going spare by the barrel and the mould went mad for it.
And the strain that made mass production possible came off a cantaloupe from a market there, 1943, carried in by a lab assistant they called Mouldy Mary who made a job of collecting spoiled fruit. A melon nobody would eat. Anyway — every kitchen I've worked in throws that liquid out.
They burst. That's the end of it — a staph cell sitting in penicillin swells and splits at the seam. The wall around a bacterium isn't a finished thing; it's being stitched shut all the time as the cell grows, and penicillin blocks the…
The other half of it was plumbing. Flasks gave you a thin film on the surface, so Peoria went to deep tanks and pumped sterile air through the broth — needed filters, impellers, a lot of valves. Once you could aerate a 25,000-gallon tank, the mould did the rest.
Corn steep liquor is mostly what the mould wants anyway — amino acids and a bit of sugar, already broken down, so it doesn't have to work for its dinner. Yields went up roughly tenfold with it. And a cantaloupe nobody would eat did the rest. I'm glad someone was paid to bring in spoiled fruit.